1. Field of the Invention
The field of the present invention relates generally to Jars and more particularly to Jars useful in wells for producing hydrocarbons and other earth fluids.
2. Background Art
Earth bore holes or wells may be formed for many useful purposes including the production of hydrocarbons or other well fluids from subsurface formations. Due to the manner or nature of the formation of such wells, access to the well below the earth surface is severely limited. During drilling or use of wells, various well tools or apparatus may become lodged or stuck at a subsurface location. In addition, it may become desirable to deliver an impact or blow of substantial force at a subsurface location in the well for other purposes. To free a stuck well tool or otherwise deliver such a blow for any desired purpose, special well tools, generically known as jars, have been developed. In general, jars use the sudden release of tension or compression energy built up in a connected wire line or well conduit to deliver the desired blow. Both well pipe string or wire line mounting and actuation of jars is known and commercial accepted conventional practice. Jars are also frequently used in well fishing operations to recover a lost tool or subject, known as a fish, from the well.
Jars are sometimes confused with structurally similar well tools called bumper subs that have an entirely different purpose. A bumper sub is a well tool that forms part of the rotary drill pipe used in well drilling operations from a floating vessel. The bumper sub provides a splined longitudinal slip joint to maintain the rotating drill bit in contact with the bottom of the bore hole by compensating for the up and down motion of the floating drilling vessel.
Under the patent office subject matter classification system issued patents claiming jarring tools may be located in class 166 (wells) or class 175 (boring or penetrating the earth). Such jar tools or below ground hammer or impact apparatus may be made responsive in operation to actuation by various types of manipulation such as a relative rotational movement. Due to the numerous thread connections and the torsional strain or elasticity in the tubular string mounting a jar, rotational control or actuation of a jarring tool is not as precise or certain as desired. For these reasons, jars are preferably triggered or actuated by a longitudinally applied push or pull force. Such longitudinal force may result from either the application of a specified weight force to the jar tool (compression) or by the application of a specific tension or upward pull on the wire line or well tubing string. These trigger forces can be easily controlled and monitored at the earth's surface by the operator with conventional drill string weight monitoring or indicating equipment. To prevent inadvertent operation of the jar, the trigger forces are normally in excess of those usually applied to the jar during routine well operation and the resulting jar impact can be directed either upwardly or downwardly. Some jars are arranged to deliver blows in both directions.
An example of a fluid operated jar is disclosed in U.S. Pat. No. 4,524,838 to Sutliff. Fluid is trapped in an expansible chamber to enable an energy build up. When the fluid is released, operation of the jar converts the energy of the wire line or well string into the desired jarring blow.
Because of the size limitations resulting from bore hole dimensions, fluid operated jars have been widely used. Large hammer forces can be repeatedly generated with a minimum of tool diameter and tool wall thickness, thereby reducing the adverse effects of employing a jar in the tubular string. The severe operating conditions experienced by jars downhole may result in seal failure. Because a seal failure will render such trapped fluid operated jar devices inoperative they have not been as reliable as many operators have desired. Also, fluid operated jars are usually limited to jarring in a single direction.
As disclosed in the Sutliff Patent, drillers or operators have found it useful in jarring operations to occasionally alternate successively upward jarring blows with a downward jarring blow. This technique, known as "spudding" is sometimes used when a keyhole slot condition is encountered. In addition, in cocking or resetting a jar that can deliver a blow in either direction, a blow in the undesired direction may inadvertently result. As this can result in well tool damage or creation of a fish, this is not a desirable feature or characteristic. More importantly, the sequence of alternate direction blows is often off-setting and may result in a self-defeating failure to accomplish the intended purpose or task.
In U.S. Pat. No. 2,241,477 to Rasmussen a mechanically operated well jar apparatus for delivering a relatively light impact for wireline operations is disclosed. A radially yieldable member controls the relative telescoping movement of the outer tubular member and the inner mandrel. As a predetermined wire line tension energy level, the longitudinally slotted outer tubular body providing the detente expands radially outwardly adjacent an annular slip shoulder to release the inner mandrel. The released mandrel moves upwardly to deliver an upwardly directed blow to the impact collar of the outer tubular member. The jar is reset by slacking off on the wireline for enabling the delivery of repeated upwardly directed blows. Also disclosed is an adjustable impact jar embodiment having a helical thread arrangement on the mandrel to control the strength or magnitude of the jarring energy by varying the stroke distance between the hammer and anvil.
An object of the present invention is to provide a new and improved jar apparatus for use in wells.
A further object of the present invention is to provide a new and improved jar apparatus for use in wells having a minimum of parts.
Yet another object of the present invention is to provide a new and improved jar apparatus that may be easily controlled to avoid a blow in an undesired direction.